Line a large cookie sheet (17.25 x 14.9 inch) with parchment paper and spray with nonstick cooking spray. This stuff is sticky and we want to be extra safe in making sure it will release from the pan.
In a medium saucepan, stir together the sugar, corn syrup water and salt then bring to a boil over medium heat. Hook the candy thermometer to the inside of the saucepan.
When the sugar comes to a boil (about 6 to 7 minutes) add the sliced butter. Stir to combine.
Let the mixture come back up to a boil until it reaches 280°F. Then stir in the peanuts.
Continue boiling the mixture until the candy thermometer reads 300°F.
Remove from heat and stir in the baking soda.
Immediately pour the mixture into the prepared cookie sheet and smooth it out.